It has conventionally been known that making metal particles small to be nano-sized presents functions that are not observed when it is in a bulk state, and “localized plasmon resonance” is in particular expected for application. Plasmon is a compressional wave of free electrons that arises by collective oscillation of the free electrons in a metallic nanostructure.
In recent years, a field of art handling the plasmon is referred to as “plasmonics” and attracts large attention, and has also been actively studied and such study includes exploiting phenomena of localized plasmon resonance of a metal nanoparticle to be intended for improvements of light-emitting devices in luminous efficiency.
For example, Japanese Patent Laying-Open No. 2007-139540 (PTD 1) discloses a technique exploiting localized plasmon resonance for enhanced fluorescence of fluorescent substance, and Japanese Patent Laying-Open No. 2010-238775 (PTD 2) discloses an electroluminescence device (EL device) in which core shell type fine particles, each composed of a fine metal particle core and an insulator shell covering the core, capable of inducing localized plasmon are arranged in a vicinity of or inside a light emitting region. Furthermore, T. Fukuura and M. Kawasaki, “Long Range Enhancement of Molecular Fluorescence by Closely Packed Submicro-scale Ag Islands”, e-Journal of Surface Science and Nanotechnology, 2009, 7, 653 (NPD 1) indicates a study on localized plasmon resonance of silver nanoparticles.
On the other hand, a “quantum dot” which may exhibit a significantly high quantum efficiency in principle attracts attention in recent years as a luminescent material for an EL device (for example, Japanese Patent Laying-Open No. 2008-214363 (PTD 3)).